1. Field of the Invention
The present invention relates to an electrophotographic image-forming member used in the field of image formation, which has a sensitivity to electromagnetic waves such as light (herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays, gamma-rays, and the like).
2. Description of the Prior Art
Se, Se-Te, CdS, ZnO, and organic photoconductive materials such as PVCz, TNF, and the like are well known as a photoconductive material constituting a photoconductive layer in an electrophotographic image-forming member. As disclosed, for example, German Laid-open Patent Application Nos. 2746967 and 2855718, amorphous silicon (hereinafter referred to as a-Si) has recently attracted attention as a possible photoconductive material in view of advantages that a-Si has comparable characteristics to other photoconductive materials in photosensitivity, spectral wave region, response to light, dark resistance, and the like. In addition, it as no harm to human bodies during usage and is easily capable of controlling p-n in spite of amorphism.
As mentioned above, a-Si has various superior charcteristics to other photoconductive materials, the practical application of which as an electrophotographic image-forming member is under rapid development, although there still remain some points to be solved.
For example, in some cases, when applied in an image-forming member for electrophotography, residual potential is observed to remain during use thereof. Therefore, when such image-forming member is repeatedly used for a long time, there is caused an accumulation of electrical or photoconductive fatigue which causes the so-called ghost phenomenon. In other words, there occur problems such as whitening in transferred images and the like.
Further, when preparing a photoconductive layer having a thickness of ten and several microns or more, after taking out the photoconductive member having such thick photoconductive layer from a vacuum-deposition chamber, the photoconductive layer tends to separate from or peel off the surface of the substrate, on which the photoconductive layer is laid, or to crack with the passage of time. These phenomena are problems to be solved in view toward storage stability, since these phenomena frequently occur in the case of a cylindrical substrate used generally in the field of electrophotography, or the like.
Further, according to the experience of the present inventors from a number of experiments, a-Si material constituting the photoconductive layer of an image-forming member for electrophotography, while it has a number of advantages, as compared with Se, CdS, ZnO or organic photoconductive materials such as PVCz or TNF of prior art, is also found to have several problems to be solved. Namely, when charging treatment is applied for formation of electrostatic images on the photoconductive layer of an image-forming member for electrophotography having a photoconductive member constituted of a mono-layer of a-Si which has been endowed with characteristics for use in a solar battery of the prior art, dark decay is markedly rapid, so that it is difficult to use conventional photographic methods. This tendency is further pronounced under a humid atmosphere to such an extent in some cases that no charge is retained at all before development.
Thus, it is required in designing of a photoconductive material to make efforts to obtain desirable electrical, optical, and photoconductive characteristics along with the improvement of a-Si materials per se and to obtain stable image quality with high sensitivity.
In view of the above-mentioned points, the present invention has succeeded in establishing, as a result of extensive and difficult studies, a relationship between a photoconductive layer and a substrate on which the photoconductive layer is laid from the standpoints of mechanical, electrical, photoconductive, and durable charcteristics of the photoconductive layer itself. This was established where the photoconductive layer is prepared with an amorphous material [hereinafter referred to as a-Si(H, X)] which contains at least one of hydrogen atom (H) and halogen atom (X) in a matrix of silicon atom.
In other words, the present inventors observed that a large strain is generated in the layer of a-Si(H, X) upon formation, and that the strain causes separation from, or peeling from a surface of a substrate, on which the layer is laid, or cracking. On account of this, they have found it necessary to eliminate the above-mentioned disadvantages such that the strain in the formed layer is removed or relaxed to the extent that it has no effect on the layer by any means, that mechanical and electrical contact between the substrate and the layer of a-Si is optimized, that closeness between them is improved, and that the optimum conditions satisfying concurrently the above-mentioned requires are provided for obtaining an electrophotographic image-forming member having excellent durability. Establishment of such optimum conditions has been accomplished as a result of extensive and strenuous studies.